Increasingly sophisticated measurements of cardiac action potentials and ventricular deformations in the beating heart have revealed complex three- dimensional patterns of electrical activation and accompanying mechanical strains. In the normal heart these patterns are associated with the complex geometry, fiber architecture and properties of ventricular myocardium. Under pathophysiologic conditions such as arrhythmia and regional ischemia, complex localized changes occur in the mechanical and electrical function of the heart emphasizing the need for more comprehensive measurements of function. In a continuum mechanics approach to understanding cardiac dynamics, electric potential and finite strain components are dependent field variables that vary continuously as a function of time and from point to point in the ventricular wall. To accurately assess these distributed variables, arrays of measuring devices are needed. In electrophysiology mapping studies have utilized increasingly dense arrays of electrodes implanted on the ventricular surfaces and across the wall to quantify the normal propagating wave of electrical activation and to study the complex disturbances caused around sites of arrhythmogenesis. Independently, cardiac strain measurements have been extended from uniaxial measurements using pairs of transducers to the measurement of two- and three-dimensional finite deformations from arrays of implanted sonomicrometers or radiopaque markers. Nevertheless, all cardiac strain measurements made previously have been discrete measurements of one- or multi-dimensional strains, i.e., one or more components of strain in the neighborhood of a point in the heart wall. These electro- mechanical arrays simultaneously measure continuous spatial distributions of both local electric potential and two-dimensional finite deformations across ventricular surfaces that are accurately reconstructed using biplane cineradiography from the three-dimensional positions of the electrodes. The proposed research would extend and generalize our measurements of two- and three-dimensional cardiac finite strains from discrete measurements using three and four point homogenous strain analyses to continuous spatial variations in strains and electrical potentials computed using finite element interpolation of the array data. The primary objectives of these proposed studies are to understand the relation between the size (number and area) of the electro-mechanical array, the sampling rates for both electrical activity and mechanical strains, and the accuracy of measurements of these distributed variables; to relate the wave of electrical activation to the distribution of times at which significant strain components are observed; and to use the array to better observe and understand the mechanisms of regional alterations in function associated with localized arrhythmia and acute ischemia.